1. Field
The following description relates to a method of estimating a round-trip time (RTT) in a content-centric network (CCN).
2. Description of Related Art
Transmission control protocol (TCP)-based data packet networks are being used in computing environments. TCP is a fundamental protocol within an Internet architecture that manages transmission of data packets within a data network. In TCP-based data networks, a user or a consumer of content may merely receive the content by explicitly requesting the content from an Internet protocol (IP) address associated with a physical device or a location. However, the above restrictive addressing scheme may have inadequate performance for fast growing network demands.
Furthermore, in TCP-based data packet networks, a request may be sent by the consumer or the user of the content, to receive the content. The request may reach a content server in a network. The content server may send the requested content to the consumer. However, in such an approach, for every access of content, the network architecture may require that a new request is to be sent by the consumer to a server, to receive the requested content. As an alternative to existing TCP-based data packet networks, content-centric networking (CCN) or named data networking (NDN) has been developed. The CCN may be an alternative approach to providing an architecture for computer networks, and may provide a new networking principle for efficient information sharing using content names that may be used instead of a host addresses of an IP to identify content that is to be shared.
The CCN may allow a user to focus on data requested by the user, rather than having to provide a predetermined reference location, for example, a physical location from which content is received.
In the CCN, a requested packet may be referred to as an interest, and a reply packet may be referred to as a content object. Content may be divided into chunks, or content objects of appropriate sizes. Thus, each interest may request for a chunk. A node requesting content may sequentially send a number of interest packets. Each of the interest packets may be associated with a content object. In the CCN, for every interest, at most one content object may be received. Furthermore, an interest may be sent towards a content source by applying a suitable name-based routing technique. Each of the intermediate nodes of the CCN that receives an interest packet may check for a content object in a content cache of each of the intermediate nodes. Such a content cache is known as a content store (CS). When a requested content object is found in the CS, a node may respond with by providing the content object from the CS. When the requested content object is not found in the CS, the node may forward the interest packet to a next node of the CCN, for example, an adjacent node. Before forwarding the interest packet, each of the intermediate nodes may store interest packet information in an interest table of each of the intermediate nodes. Such an interest table is known as a propagating interest table (PIT). Forwarding of information may be performed manually or by using a suitable routing technique, and may be stored in a forwarding information base (FIB) table.
A node including a content object may reply to a requester by using a reversed path formed by using entries of a PIT created at intermediate nodes. When an interest is satisfied by content, or when content passes through the intermediate nodes, an entry of the PIT may be removed at the intermediate nodes including end nodes so that the PIT contains useful information about ways to provide content.
As described above, instead of using an inefficient scheme of sending only a single interest at a time, a plurality of requests may be aggregated to form an interest packet. Interest packet requestors may request a plurality of content objects that are monitored by dynamically changing an entity, known as a window size of an interest packet, instead of requesting a single content object.
Initially, an interest packet with a window size of “w_max” may be sent. When the interest packet is received, a content sender may verify the window size of the received interest packet, and may send content to a requesting node. Additionally, interest packet information may include a segment start range. A point of first missing content may be regarded as a point in which a new interest packet is to be constructed and sent to a next node in the CCN. Accordingly, the window size of the interest packet may be reduced at each node based on content availability at each node.
In TCP-based data networks, a round-trip time (RTT) may be estimated based on a time at which a request is sent, and a time at which content associated with the request arrives. The RTT may be estimated based on a difference between the time at which the request is sent and the time at which content associated with the request arrives. Such an RTT may be calculated by using timestamps to identify when these events occur.
In a CCN, an RTT may also be estimated based on a time at which an interest is sent, and a time at which a content object associated with the request arrives. Proper RTT estimation may be required to estimate various timer values, for example, a retransmission timeout (RTO), a delayed interest timeout (DTO), and a negative acknowledgement timeout (NTO). Such timer values may be used to regulate information transmission throughout the network.
In TCP-based data networks, content may be received from a single entity, for example, a content server. A TCP node may establish an end-to-end connection with a content server to obtain content. In such a scenario, RTT estimation of a TCP network may be inherently based on an assumption that content is received by a client from the same node, namely, a content server.
In the CCN, RTT estimation of a TCP may be used. For a single interest, at most one content object may be expected to be received. Additionally, when a single interest packet requests for a plurality of pieces of content, the RTT estimation of the TCP may require predetermined modifications to obtain relevant information for deriving such RTT estimation.
Therefore, a plurality of requestors may be grouped together to form an interest packet in a CCN. Thereafter, the interest packet may be sent to obtain content associated with the plurality of requestors. However, currently, a mechanism for measuring an RTT for the CCN when using such an interest packet does not exist.